Evaluation of colorectal adenocarcinomas at single-institution with respect to microsatellite instability

Hereditary non-poliposis colorectal cancers exhibit a high rate of microsatellite instability. Comparative studies involving stage and other prognostic parameters demonstrate a better prognosis in the presence of microsatellite instability versus colon cancers without microsatellite instability. Our study included 608 cases diagnosed with colorectal adenocarcinoma by our laboratory between 2004-2010. The cases were re-evaluated with respect to criteria defined for MSI, taking into consideration age, anatomic localization, and histopathological criteria. Immunohistochemical study was performed in appropriate blocks for using MLH-1, MSH-2, MSH-6, and PMS-2. The specimens were re-evaluated according to the histological criteria defined for microsatellite instability. Anti-MLH-1, anti-MSH-2, anti-MSH-6, and anti-PMS-2 antibodies were applied to the paraffin blocks of 27 cases which presented morphological criteria suggestive of DNA repair mutation and had a high Mspath score. Immunohistochemical study with MLH-1, MSH-2, MSH-6, and PMS-2 for the analysis of mismatch repair was refined using the cases with higher Mspath scores. In this study, we reviewed the clinical and histopathological features of 608 cases with colorectal adenocarcinoma diagnosed in our laboratory between 2004-2010 and assessed pathological features in terms of microsatellite instability. The results were discussed in view of the literature.